1. Field of the Invention
The present invention generally relates to a method for the preparation of azide photo-initiators. More specifically, the present invention relates to a novel method for the preparation of N-azidosulfonyl-arylimides, which are known as photo-initiators.
2. Description of the Related Art
In the photochemical related industry, photoresist agent is the most important application. The photo image forming process makes possible the selective formation of via holes, the formation of heat and corrosion resistant protective films, dielectric films or alignment layers, in addition to the disposition of specific patterns onto substrates. Hence, photoresist agents are widely used in the manufacturing and sealing processes of ICs, and the manufacturing of LCDs and printed circuit boards.
The formula of the photoresist agent includes photo-initiators, photo-resistant agent, solvents and other additives. Among these, photo-initiators are the most expensive, the most difficult to synthesize, and have the greatest influence on the overall photosensitivity, quality and function of the agent. Generally, by exposure, the photo-initiators generate free radicals, carbene, nitrene, protons and other cations or anions to initiate the polymerization reaction and allow a subsequent series of follow-up applications.
Azide photo-initiator is one of the most important photo-initiators. By exposure to light, the Azide photo-initiator is in an excited state, in which N.sub.2 is removed to form nitrene. The high reactivity of nitrene causes difficulties in polymerization, purification, usage and storage.
Various methods for the preparation of azide photo-initiators are disclosed in U.S. Pat. No. 4,329,556 (Siemens) and D.E. Pat. No. 4,328,838 (BASF). The formulation of the photoresist agent with the azide photo-initiators is disclosed in E. Pat. No. 188,205 (Merck).
In general, the method disclosed by Siemens is by reacting 4-acetamidobenzenesulfonyl chloride and CH.sub.2 Cl.sub.2 solvent under the presence of the dehydrating agent N,N'-dicyclohexylcarbodiimide (DCC) to carry out the polymerization. The DCC is high-priced and moisture absorbing, hence it is hard to manage. Similarly, CH.sub.2 Cl.sub.2, being regulated, is not easy to use and manufacture in Taiwan. Since the purification of product is done by chromatography, which lowers product yield to 30%, it is hard to achieve mass production.
The BASF method discloses a process in which N-phenylmaleimide, which is 10 times the price of the 4-acetamidobenzenesulfonyl chloride (310 U.S.$/kg vs. 30 U.S.$/kg), is utilized as a reactant. Moreover, as the polymerization reaction is carried out by sulfonyl chloride, problems such as waste acids and wastewater arise, making this method dirty and non-environmentally friendly.